The Global System for Mobile communications (GSM) is a commonly used standard for mobile telephony. A GSM subscriber can connect to a GSM network using her terminal via a Mobile Switching Centre Server (MSC), which provides circuit switched calling, packet switched services, mobility management and other GSM services to the user terminal.
When a GSM subscriber attaches to a MSC, a Base Station Controller (BSC) in the radio access network reports the cell in which the subscriber resides to the MSC. The BSC also reports the current cell to the MSC when, for example, the subscriber's mobile station performs a periodic location update procedure, when the subscriber initiates a GSM service, and when the subscriber changes position to another location area. The MSC may use internal mapping to associate a location identifier (or location number) with the subscriber's current cell. The location number indicates the physical or geographic location of the subscriber, and can be used by the MSC and by Value Added Services (VAS). Examples of VAS that use the subscriber's location for service logic processing include Home zone, Office zone and Location based charging. Often, a Public Land Mobile Network (PLMN) operator uses E.164 numbers as the location numbers. Where this is done, the operator defines a number plan for its radio access network, and each location area within this radio access network has a location number associated with it. A location area may be a single GSM cell or a group of cells, as defined by the operator. A location number is similar to a fixed network number. For example, a Public Switched Telephone Network (PSTN) number can be used to identify, to some extent, the subscriber's location. Generic Access Network (GAN) allows GSM subscribers to gain access to a GSM network using unlicensed spectrum, such as Wireless LAN and Bluetooth. GAN is the formal term used by 3GPP; but this technology is more commonly known under the name Unlicensed Mobile Access (UMA). The term UMA is used in the remainder of the present document, and can be taken to refer to either Unlicensed Mobile Access or Generic Access Network. Access to a GSM network using UMA is normally done using a terminal supporting both regular GSM access and UMA access. Such a terminal is referred to herein as a UMA terminal. UMA allows a subscriber having a UMA terminal to perform a handover between GSM access and WLAN access, both during a call and outside a call.
When a GSM subscriber attaches to a GSM network using a UMA terminal, there is at present no defined mechanism for the MSC to associate a location number to the current location of the subscriber. This is because a Generic Access Network Controller (GANC), acting as a BSC, does not report a ‘cell’ to the MSC, related to the subscriber's current access, and so the MSC cannot use its regular method to derive a location number.
A UMA subscriber may access a GSM network through a home WLAN access point, connected to a Digital Subscriber Line (DSL). The DSL connection provides IP connectivity. The UMA terminal, in turn, uses the IP connectivity to register with the GANC, which then registers the subscriber with the MSC. In the case where a subscriber uses UMA to access a GSM network through DSL, it would be desirable to be able to assign the DSL line number as the location number for that subscriber. For example, when the subscriber uses UMA to access a GSM network via DSL, her location could be determined by the DSL line identity. Similarly, when a subscriber uses UMA through a Wireless Local Area Network (WLAN) access at home, and that subscriber's PSTN number at home is +46 26 157000, then her location number for the purpose of UMA access would be +46 26 157000.
When a service such as Virtual Private Network (VPN) is controlling a call to or from that subscriber, the VPN service could receive the current location number of that subscriber. If the reported location number is, for example, +46 26 157000, then the VPN would be aware that the subscriber is connected to the network using her home WLAN/DSL, provided that the VPN can deduce from the reported location number (+46 26 157000) that the subscriber's current location is served by a GANC. It will be described below how a location number is associated with a GANC.
Having a location number available when using UMA access is required for emergency calls. Operators are forced by law to provide the location of a calling subscriber when the subscriber establishes an emergency call. Furthermore, Lawful Intercept (LI) systems often need to be able to determine a calling person's or called person's location. A solution to this problem is provided by WO 2007/048028, although this involves communicating with a Serving Mobile Location Centre. The SMLC must send a positioning request to a database and calculate the location using the received information. This requires bandwidth and processor use for each location request. Another solution in the context of an IP Multimedia Subsystem (IMS) network is to query a Connectivity Session Location and Repository Function (CLF) using a Media Access Control (MAC) address of an access point. However, the MAC address can be easily changed and so the MAC address cannot be associated with location information with any certainty.